1. Field of the Invention
The present invention relates to a driving method for an AC (Alternating Current) type plasma display panel having a large range of a sustaining voltage and capable of being driven by a low voltage.
The present application claims priority of Japanese Patent Application No. 2001-356997 filed on Nov. 22, 2001, which is hereby incorporated by reference.
2. Description of Related Art
Generally, a plasma display panel (PDP) has many characteristics, for example, the PDP is thin and can perform large screen display easily, an angle of visibility is wide, and a response speed is fast. Therefore, the PDP is recently used as a flat panel display such as a wall-mounted television or a public display panel and a like. Based on driving methods, PDPs are divided into two types including a direct current type discharge PDP (a DC-type PDP) driven by exposing electrodes to a discharge space filled with a discharge gas so as to generate a direct current discharge between the electrodes and an alternating current type discharge PDP (an AC-type PDP) driven in a state of an alternating current discharge without directly exposing electrodes to the discharge gas by coating a dielectric layer on the electrodes. In the DC-type PDP, the discharge continues when a voltage is applied, and in the AC-type PDP, the discharge continues by reversing a polarity of the voltage. Also, AC-type PDPs are divided into two types including one having two electrodes in one picture cell and the other having three electrodes in one picture cell. The PDPs having these structures are described in a document, for example, in “Society for Information Display '98 Digest, pp. 279-281, May, 1998”.
Next, explanations will be given of a structure and a driving method of a conventional three-electrode AC-type PDP. FIG. 7 is a sectional view showing a cell structure of the conventional three-electrode AC-type PDP. FIG. 8 is a plan view showing an electrode arrangement of the conventional three-electrode AC-type PDP.
As shown in FIG. 7, the conventional three-electrode AC-type PDP is provided with a front substrate 20, and a rear substrate 21 opposite to the front substrate 20. The front substrate 20 and the rear substrate 21 are made of glass or a like. A plurality of scanning electrodes 22 and a plurality of common electrodes 23 are alternately arranged in parallel at a predetermined intervals on a surface opposite to the rear substrate 21 in the front substrate 20. The scanning electrodes 22 and the common electrodes 23 are transparent electrodes made of ITO (Indium Tin Oxide) or a like, and extend from the back to the front in FIG. 7.
Metal electrode 32 is laminated on each of the scanning electrode 22 and the common electrode 23 to reduce wring resistance. Also, a transparent dielectric layer 24 is provided to cover the scanning electrode 22 and the common electrode 23, and a protection layer 25 made of MgO or a like is formed on the transparent dielectric layer 24.
A plurality of data electrodes 29 are provided on a surface opposite to the front substrate 20 in the rear substrate 21. Each of the data electrodes 29 extends in a direction orthogonal to the scanning electrodes 22 and the common electrodes 23 (in a longitudinal direction in FIG. 7). A white dielectric layer 28 and a fluorescent layer 27 are provided on the data electrodes 29.
A partition (not shown) is provided between the front substrate 20 and the rear substrate 21. The partition is provided in a grid array viewed from a direction orthogonal to a surface of the front substrate 20 and divides a discharge space 26 into picture cells (display cells). In each picture cell 31 (shown in FIG. 8), each scanning electrode 22, each common electrode 23 and each data electrode 29 are introduced, and a closest point to the scanning electrode 22 in the data electrode 29 and a closest portion to the common electrode 23 in the data electrode 29 are included. In the discharge space 26, a mixed gas such as He, Ne, and Xe is filled as a discharge gas.
As shown in FIG. 8, in a display screen 30 of the PDP, picture cells 31 are arranged in a matrix so as to include respective closest portions of the scanning electrodes 22 (Si (i equals 1 to m)) and the common electrodes 23 (Ci (i equals 1 to m)) to the data electrodes 29 (Dj (j equals 1 to n)). A discharge gap 37 for generating surface discharge is arranged between the scanning electrode Si and the common electrode Ci, and a non-discharge gap 38 for generating no surface discharge is arranged between the scanning electrode Si and the common electrode Ci−1.
Next, a driving method for the conventional three-electrode AC-type PDP will be explained. Conventionally, a main three-electrode AC-type PDP driving method is a scanning-displaying separation (ADS technique). The driving method of the scanning-displaying technique will be explained. FIG. 9 is a waveform view showing the conventional three-electrode AC-type PDP driving method. FIG. 10A to FIG. 10E are sectional schematic views showing the conventional PDP driving method. In FIG. 10A to FIG. 10E, positive wall charges 35 and negative wall charges 36 are represented by various polygonal figures, and heights of the positive wall charges 35 and the negative wall charges 36 represent levels of wall voltages caused in dielectric layers by wall charges.
As shown in FIG. 9, in the three-electrode AC-type PDP driving method, a field includes a plurality of sub-fields, and one sub-field 8 includes three periods, namely, a primary discharge period 7, a scanning period 5 and a sustaining period 6.
First, the primary discharge period 7 will be explained. At a start point of the primary discharge period 7, caused by a discharge in a previous sub-field 1 before the sub-field 8, a wall charge builds up on the dielectric layers in the picture cell 31. A building-up state of the wall charge changes based on whether the picture cell 31 is lit up or not in the previous sub-field 1. The primary discharge period 7 initializes the wall charge and generates a priming effect for making a charge easily when data is linear-sequentially written based on display data in following process.
The primary discharge period 7 includes a sustaining erasing period 2, a priming period 3 and a priming erasing period 4. In the sustaining erasing period 2, a discharge is generated in the display call 31 in which a sustaining discharge has been generated in the previous sub-field 1. The display call 31 in which the sustaining discharge is generated in the previous sub-field 1 is in a state of a wall charge arrangement as shown in FIG. 10A by a last sustaining pulse in the previous sub-field 1, namely, in a wall charge arrangement in which a negative wall charge 36 builds up over the scanning electrode 22 and on a surface of the transparent dielectric layer 24 (hereinafter, may be referred to as “over the scanning electrode S”), and positive wall charge 35 builds up over the common electrode 23 and on a surface of the transparent dielectric layer 24 (hereinafter, may be referred to as “over the common electrode C”), and over the data electrode 29 and on a surface of the white dielectric layer 28 (hereinafter, may be referred to as “over the data electrode D”).
In this state, the previous sub-field 1 moves to the sustaining erasing period 2 in the primary discharge period 7. In the sustaining erasing period 2, the electric potential of the scanning electrode S and that of the data electrode D are set to the ground potential, and a positive electric potential Vs is applied to the common electrode C. With this operation, a potential difference between the scanning electrode S and the common electrode C becomes large gradually, and a weak discharge occurs between the scanning electrode S and the common electrode C. Then, as shown in FIG. 10B, a wall charge, close to the discharge gap 37, building up between the scanning electrode S and the common electrode C changes.
On the other hand, a wall charge arrangement in which no discharge occurs is accomplished in the display call 31 as shown in FIG. 10B before moving to the sustaining erasing period 2, and no discharge occurs during the sustaining erasing period 2. Therefore, at an end of the sustaining erasing period 2, each display call 31 is put in a state of wall charge arrangement as shown in FIG. 10B regardless of lighting up or not in the previous sub-field 1. In other words, each display call 31 is initialized.
In the priming period 3, a priming discharge is generated to generate a writing discharge at a low voltage in the scanning period 5 which will be described later, and the priming effect is obtained. As shown in FIG. 9, in the priming period 3, a positive ramp waveform increasing continuously from a predetermined positive electric potential to a specified voltage Vp in the scanning electrode S is applied and a ground potential is applied to the common electrode C and to the data electrode D. With this operation, a weak discharge is generated between the scanning electrode S and the common electrode C, a wall charge arrangement is accomplished in which wall charges are large at an edge portion on the scanning electrode S facing the common electrode C and at an edge over the common electrode C facing the scanning electrode S as shown in FIG. 10C.
Then, in the priming erasing period 4, while the ground potential is applied to the data electrode D, a voltage Vs is applied to the common electrode C. The electric potential of the scanning electrode S is continuously decreased from a predetermined electric potential. With this operation, a weak discharge occurs to return the wall charge building up in the priming period 3, and the wall charge arrangement is returned to a state as shown in FIG. 10D. Then, the primary discharge period 7 is finished.
In the scanning period 5, a positive voltage Vbw is applied to the scanning electrode S, and a positive voltage Vsw is applied to the common electrode C. Then, by sequentially setting electric potentials of the scanning electrode S1 to the scanning electrode Sm to the ground potential, a scanning pulse 9 is sequentially applied to the scanning electrode S1 to the scanning electrode Sm. A data pulse 10 is selectively applied to the data electrode D1 to the data electrode Dm so as to match with timing of the scanning pulse 9 based on the display data.
In a display call 31 where the data pulse 10 is applied to the data electrode D, a potential difference between the scanning electrode S and the data electrode D (hereinafter, maybe referred to as an opposition space) exceeds a firing voltage of the opposition space. Therefore, a writing discharge occurs in the opposition space, and a large positive wall charge builds up over the scanning electrode S. Also, with this discharge, in a space between the common electrode C and scanning electrode S (hereinafter, may be referred to as a surface space), the space to which the positive voltage Vsw is applied and is large biased to the positive electric potential, the charge moves, and a wall charge arrangement as shown in FIG. 10E is accomplished. In contrast with this, in a display call 31 where no data pulse 10 is applied, no writing discharge occurs, on the grounds that the potential difference across the opposition space does not achieve to the firing voltage, and therefore, there is no change in the wall charge arrangement. As described above, by the existence of the data pulse 9, two types of wall charge arrangements can be accomplished. Oblique lines of the data pulse 10 in FIG. 9 represent that existences of the data pulse 10 are changed by the display data. After applying the scanning pulse 9 to all of the scanning electrodes S (S1 to Sm), the sustaining period 6 starts. In the sustaining period 6, a sustaining pulse is alternately applied to all of the scanning electrodes S and to all of the common electrodes C. The voltage Vs of the sustaining pulse is set lower than the surface firing voltage. In a display call 31 where the writing discharge occurs, as shown in FIG. 10, since a positive wall charge builds up over the scanning electrode S and a negative wall charge builds up over the common electrode C, a wall voltage is generated in a surface space (between the scanning electrode S and the common electrode C). Therefore, when a first positive sustaining pulse (a first sustaining pulse) is applied to the scanning electrode S, the wall voltage is superimposed on the first positive sustaining pulse, the potential difference of the surface space becomes greater than the firing voltage, and the sustaining discharge occurs. With this sustaining discharge, a negative wall charge builds up over the scanning electrode S, and a positive wall charge build up over the common electrode C. When a second positive sustaining pulse (a second sustaining pulse) is applied to the common electrode C, the wall voltage is superimposed on the second positive sustaining pulse, and the sustaining discharge occurs again. As a result, when the first sustaining pulse generates, wall charges having reverse polarity are stored over the scanning electrode S and over the common electrode C. After this, by alternately applying the sustaining pulse to the scanning electrode S and the common electrode C, the sustaining discharge occurs contentiously by the same operation. In other words, a wall voltage caused by a wall charge building up through a x-th sustaining discharge is superimposed on a (xplus1)-th sustaining pulse, and the sustaining discharge is continued. A luminescence amount is determined by a number of times of sustaining discharges.
On the other hand, in a display call 31 where no writing discharge occurs in the scanning period 5, no wall charge is superimposed on the sustaining pulse. As described above, since only the sustaining pulse cannot achieve the firing voltage, no sustaining discharge occurs.
A group of the primary discharge period 7, the scanning period 5, and the sustaining period 6 is called the sub-field 8. When an image is displayed on the three electrode AC-type PDP, in one field to be a period for displaying image information for one display call 31, numbers of sustaining pulses in respective sub-fields are made different one another, it is selected whether each sub-field is lit up or not, and a number of sustaining discharges is controlled, thereby performing image gradation display.
However, the above-described method has the following problems. In the above-described conventional three-electrode AC-type PDP driving method, since a number of power sources for driving is decreased with possibility, setting voltages for respective pulses in the driving waveform are set commonly with possibility. Therefore, the common electrode potential in the sustaining erasing period 2 and the priming erasing period 4 is set to be equal to the sustaining voltage Vs. However, the sustaining voltage Vs is set lower than the surface firing voltage in each display call 31 of the three-electrode AC-type PDP. Therefore, the discharge is insufficient in the priming erasing period 4, and a size of the wall charge building up at the end portion of the scanning electrode S close to the common electrode C is not equal to a size of the wall charge building up at the end portion of the common electrode C close to the scanning electrode S. In other words, the wall charges, close to the discharge gap 37, building up between the common electrode C and the scanning electrode S are not equal.
As a result, in a display call 31 which is not lit up, an error discharge of the sustaining discharge is apt to generate. Therefore, it is impossible to set the sustaining voltage Vs at a high level. As a result, there are problems in that the discharge is still insufficient in the priming erasing period 4 and in that a driving margin (range) of the sustaining voltage Vs becomes limited and when the sustaining voltage Vs varies, the operation of the PDP becomes unstable.
Also, in the above-described conventional three-electrode AC-type PDP driving method, there is another problem in that the data pulse voltage is high such as 70V and a driving cost is high, thus requiring reduction of power consumption.